•Fill the gap in the effect of stand density on microbial compositions.•The effect of stand density on fungi was higher than on bacteria.•Low-density plantations showed higher microbial diversity and ...richness.•Ascomycota and Basidiomycota were key species in response to stand density.
Despite recent improvements in understanding the composition of microbial communities in forest soils, fundamental questions regarding how their dynamics and function vary with forest management strategies, such as stand density, and the factors that affect them are still unclear. In this study, the spectrophotometry and high-throughput sequencing technology were used to determine enzyme activities and microbial community composition in the topsoil (0–20 cm) of 35-year-old Chinese fir plantations with five stand densities. The results showed that stand density had significant effects on soil fungal community composition and diversity and the activity of catalase and sucrase. However, stand density had no significant effects on the bacterial communities, although the diversity of the bacterial communities varied with stand density. Overall, the increase in stand density reduced the activities of catalase, urease and surase and the Chao1 and Shannon diversity of bacterial and fungal communities. We found that positive correlations between enzyme activities and microbial diversity indices were significant. We also found that bacterial community compositions were significantly influenced by pH, alkali available N, available P and available K, and that fungal community composition was significantly influenced by pH, soil moisture, total N, alkali available N, available P and available K. Our results provide important insights into the effect of stand density on soil enzyme activities and microbial community composition, which is certainly significant for developing stand density regulation strategies to mitigate the effects of degradation of soil biological activities.
•Reduced irrigation decreased SWC, LAI, biomass, yield and ET, but improved WUE.•Increasing planting density increased LAI and ET, but reduced SWC and biomass.•Planting density had significant ...effects on yield and WUE.•MI-D2 is recommended for spring maize production in the Northwest China.
The limited availability of water resources severely restricts agricultural development in the semiarid and arid regions of Northwest China. A two-year field experiment was conducted to investigate the effects of irrigation and planting density on the soil water content (SWC), growth and development, yield, water use efficiency (WUE) and economic benefits of spring maize in arid areas under mulch drip irrigation system. The optimized combination of irrigation and planting densities for high grain yield, WUE and net return were obtained by multiple regression analysis. Experiment included three irrigation treatments (HI: 450 mm; MI: 337.5 mm; LI: 225 mm) and four planting densities (D1: 75,000 plants ha−1; D2: 90,000 plants ha−1; D3: 105,000 plants ha−1; D4: 120,000 plants ha−1). The results showed that the reduction of irrigation decreased SWC, leaf area index (LAI), aboveground biomass, yield and evapotranspiration (ET), but improved WUE. HI and MI were significantly different from LI. Increasing planting density increased LAI and ET, but reduced SWC and aboveground biomass. Planting density had significant effects on yield and WUE, which differed in both years. The overall yield, WUE and net return were greater than the two-year average of HI-D1 under an irrigation amount of 271.9–500.2 mm and a planting density range of 7.1–14.3 × 104 plants ha-1. MI-D2, with 25 % reduced irrigation, increased the two-year average yield, WUE and net return by 5.2 %, 20.2 % and 27.2 %, respectively, compared to HI-D1. Therefore, irrigation of 337.5 mm at a medium planting density of 90,000 plants ha-1 under mulch drip irrigation is recommended for spring maize production in the drylands of Northwest China in our research.
The Chinese government regards ensuring food security and developing water‐saving agriculture as an important national strategy and that carrying out relevant research has important practical ...significance and production application value. A two‐year field experiment was conducted to explore the compensation potential in rice yield by using rice varieties with different panicle size under two water management regimes (conventional water management or CWM and alternate wetting and drying or AWD). The results showed that the large panicle rice variety resulted in greater yield, crop water productivity, spikelet density, dry matter accumulation and translocation, and photosynthesis. Compared with the CWM, the AWD had little effect on rice yield. However, with an appropriate planting density, the AWD achieved a greater grain yield compared with the CWM. Moreover, the AWD increased crop water productivity and the grain‐filling efficiency. The loss of spikelets under the AWD could be compensated by increasing the planting density. Although AWD reduced tillering number, it increased the photosynthetic rate, dry matter accumulation and its translocation to grain, and leaf area index. In addition, the adverse effects on rice growth and the yield caused by the AWD could be alleviated by increasing planting density of rice. Therefore, an appropriate planting density can be used to save water and maintain high grain yield of rice under alternate wetting and drying.
Increasing rice planting density can compensate for the negative impact of AWD on yield by increasing spikelets density, which may be a way to eliminate the risk of AWD reducing yield.
•The 3-PG model simulated the growth dynamic of Chinese fir plantations under various initial planting densities in southern China.•The sensitivity of FR, alphaCx and gammaN1 parameters influenced by ...stand age and initial density variations.•Stand DBH and tree height at high initial densities increased sharply after the onset of self-thinning.
Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is the most widely distributed conifer species in the subtropical region of southern China. Due to its ecological and economic significance, accurate prediction of growth of Chinese fir plantations is crucial for forest management and industrial timber production. In this study, we employed a physiologically process-based model (3-PG) to simulate the growth dynamic of Chinese fir plantations under various initial planting densities in southern China. Calibration and validation results indicated that the model outputs have strong correlations with the observed data (R2 > 0.79, p < 0.01), except foliage biomass and root biomass. Self-thinning will occur earlier at higher initial planting densities, and stand DBH and height will increase dramatically afterwards. Sensitivity analysis further revealed that the FR (soil fertility rating), alphaCx and gammaN1 parameters were highly sensitive in the 3-PG model (p < 0.01), while their sensitivity was influenced by stand age and initial density variations. This study confirmed that the parameter-specific optimized 3-PG model could accurately predict the growth process of Chinese fir plantations under different densities. It will provide a scientific reference for regional-scale management of Chinese fir plantations.
Plant population density is an important variable in agronomy and forestry and offers an experimental way to better understand plant–plant competition. We made a meta‐analysis of responses of ...even‐aged mono‐specific stands to population density by quantifying for 3 stand and 33 individual plant variables in 334 experiments how much both plant biomass and phenotypic traits change with a doubling in density. Increasing density increases standing crop per area, but decreases the mean size of its individuals, mostly through reduced tillering and branching. Among the phenotypic traits, stem diameter is negatively affected, but plant height remains remarkably similar, partly due to an increased stem length‐to‐mass ratio and partly by increased allocation to stems. The reduction in biomass is caused by a lower photosynthetic rate, mainly due to shading of part of the foliage. Total seed mass per plant is also strongly reduced, marginally by lower mass per seed, but mainly because of lower seed numbers. Plants generally have fewer shoot‐born roots, but their overall rooting depth seems hardly affected. The phenotypic plasticity responses to high densities correlate strongly with those to low light, and less with those to low nutrients, suggesting that at high density, shading affects plants more than nutrient depletion.
We present a meta‐analysis of the response of 36 stand and plant traits to increasing plant density in mono‐specific stands. High‐density plants have a phenotype similar to that of low‐light plants.
By means of meta-analyses we determined how 70 traits related to plant anatomy, morphology, chemistry, physiology, growth and reproduction are affected by daily light integral (DLI; mol photons m−2 ...d−1). A large database including 500 experiments with 760 plant species enabled us to determine generalized dose–response curves. Many traits increase with DLI in a saturating fashion. Some showed a more than 10-fold increase over the DLI range of 1–50 mol m−2 d−1, such as the number of seeds produced per plant and the actual rate of photosynthesis. Strong decreases with DLI (up to three-fold) were observed for leaf area ratio and leaf payback time. Plasticity differences among species groups were generally small compared with the overall responses to DLI. However, for a number of traits, including photosynthetic capacity and realized growth, we found woody and shade-tolerant species to have lower plasticity. We further conclude that the direction and degree of trait changes adheres with responses to plant density and to vertical light gradients within plant canopies. This synthesis provides a strong quantitative basis for understanding plant acclimation to light, from molecular to whole plant responses, but also identifies the variables that currently form weak spots in our knowledge, such as respiration and reproductive characteristics.
•Moderate plant density yielded higher cotton fiber compared to either lower or higher density.•Higher cotton yield was resulted from higher reproductive organs biomass and K acquisition.•Earlier ...sowing date could have a good harvest only accompanied with a moderate plant density.
Cotton is the fifth major oil crop and grown primarily for natural fiber globally. Suitable management practices like planting density (PD) and sowing date (SD) are the major drivers of cotton crop productivity. Cotton production with a normal practice of 3 plants m−2 in Yangtze River Valley China, resulting in an average yield of 1200kgha−1 although, high input costs and low productivity are the two major consequences in cotton production systems. The production costs can be decreased and profits can be increased through optimal PD and adjusting SD. The objectives of this study were to optimize growth, yield, biomass partitioning and potassium (K) distribution of a cotton crop under a short growing season and elevated PD. Experiments were conducted with two sowing dates i.e. early (S1, May 20 and late S2, June 04) as the main plot and three plant densities (D1, low 7.5; D2, moderate; 9.0 and D3, high; 10.5plantsm−2) as the subplot laid out in a split arrangement with four replicates. D3 crops significantly delayed cotton growth period under late sowing date compared with early planted crops. Compared with S2 crops, S1 plants produced 29% and 26% higher seed cotton and lint yield, respectively. Among the PD, D2 plants produced 12%, 15%, 13% and 6% more seed cotton yield and lint yield over D1 and D3 crops respectively. The increment in yield was due to increased plant reproductive organs biomass occasioned by moderate density and longer cropping season which allowed the utilization of available resources. Higher K acquisition i.e. (0.9VMkgha−1d−1), further improved reproductive structures formation in S1 combined with D2 crops. The S1 in combination with D2 crops resulted in the highest average (77VTkgha−1d−1) and maximum (93VMkgha−1d−1) rates of reproductive organs biomass accumulation than other combinations. Conclusively, use of medium density under both sowing dates is an effective strategy for optimal seed cotton and lint yield.
Straw returning has been widely used as a nitrogen (N) reduction measure in the North China Plain in recent years. However, little is known of the optimal planting density and N application rate of ...cotton under straw returning. In order to study the effect of the planting density and N application rate on cotton yield, nitrogen agronomic efficiency (NAE), fertilizer N recovery efficiency (FNRE), N balance and soil N under straw returning, a split-plot design in randomized complete blocks was used in the experiment. The main plots were assigned to plant densities (4.50 × 104, 6.75 × 104 and 9.00 × 104 plants hm−2), and the subplots to N application rates (0, 180, 225 and 270 kg N hm−2). The results showed that the biological yield increased as the planting density and the N application rate increase, but the harvest index decreased. Therefore, the highest biological yield was found under D9.00N270, but the highest cotton yield was found under D6.75N225. Excessive N (N270) application rate was not conducive to the improvement of NAE and FNRE. The amounts of plant N derived from fertilizer (Ndff) was reduced with the increase of planting density. Therefore, soil N would be consumed because the N balance was a negative value when N application rate was decreased at N180, especially at high density. The N balance was closest to zero at D6.75N225. In summary, with the yield, NAE, FNRE, N balance and the stability of soil N taken into consideration, the optimal combination of planting density and N application rate in the North China Plain was D6.75N225, because this treatment had the highest cotton yield, and most importantly, it maintained sustainable cotton production in the field.
•High density planting saved nitrogen fertilizer without yield reduction.•The N uptake rate from urea of cotton reduced with increased plant density.•Soil N was consumed because the negative N balance under low N rate.•High N balance followed with high FNL and low NAE under high N rate.
•Leaf area index (LAI) varied among clones but increased with planting density.•Average stand transpiration at low tree density was 40% lower (622 mm) than that exhibited by high density ...(879 mm).•Selection of clonal material and silvicultural treatments could maximize productivity while minimizing water use.•WUE were significant different among three clones, but it was not sensitive to planting density variation.
We examined the influence of stand density and genotype on transpiration and water use efficiency in high productivity plantations. Three widely planted Eucalyptus clones that differ in drought tolerance and productivity (E. urophylla, E. urophylla × E. grandis and E. grandis × E. camaldulensis, clones IP, B2 and C3, respectively) were measured at four densities (590, 1030, 1420, and 2950 trees ha−1). Over the 1-year study period (1.5–2.5 years after planting), individual biomass increment decreased with increasing density, from 21 kg tree−1 at 590 trees ha−1 to 6 kg tree−1 at 2950 trees ha−1. Stand increment typically follows the reverse pattern, increasing as density increases. This was the case for two clones (IP and B2), but stand increment was consistent across tree spacings for C3. Transpiration increased with density, from a low of 622 mm yr−1 to a high of 879 mm y−1. Some of the increased water use resulted from higher leaf area index at higher densities. The B2 clone transpired the most water on average, produced the greatest increment (23 Mg ha−1 yr−1 for 1030 trees ha−1), and produced the most wood L−1 transpiration (water use efficiency, 2.3 g biomass L−1). The clone C3 had the lowest increment (only 12 Mg ha−1 yr−1) because of the combination of low transpiration and low water use efficiency (only 1.5 g biomass L−1). Optimizing clone selection and silviculture for the combination of high yield and high water use efficiency may help reduce risks from drought as well as water conservation.
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